Increasingly, many parts of the world are growing plantation forest of Radiata Pine, Eucalyptus and other fast growing species. One of the problems with these trees and other species is that the heartwood has poor strength characteristics and is unsuitable for structural grade timber. Consequently, it is used for non-structural purposes such as pallet stock where its value is roughly one third that of structural lumber. Structural lumber is made from the outside, or sapwood of the tree. Accordingly, any structural lumber cut from flitches of these varieties, or having other heartwood deficiencies, is required to be cut by avoiding the heartwood while edge trimming the flitch. Previous edge trimmers, typically known as edgers, have not adequately addressed this difficulty.
For example, U.S. Pat. No. 4,239,072 discloses a method and apparatus for edge trimming a flitch. A number of overhead pres rolls engage the flitch as the flitch passes along a chain conveyor. The flitch is centered by sets of centering rolls. A number of scanners are positioned above the conveyor to provide a computer with appropriate information on the profile of the flitch. The edging assembly includes a pair of adjustable cutting heads designed to chip the unwanted edges from the side board. The cutting heads are dewed in a direction perpendicular to the direction of movement of the board by hydraulic cylinders so that one or more pieces of side board lumber can be cut from a single flitch.
U.S. Pat. No. 4,449,557, assigned to the same assignee as U.S. Pat. No. 4,239,072, uses substantially the same system for delivering flitches to an edging assembly as the '072 patent. However, instead of using angled edge chippers, as in the '072 patent, the '557 patent uses sawing disks or saw blades to make the edge cuts. The entire edger system moves as a unit so that the sawing disks can skew, that is change the angle between the axis of rotation of the sawing disks and the axis of rotation of the arbor on which the saw blades are mounted, and can slew, that is move laterally along a line generally parallel to the axis of rotation of the arbor.
Many conventional edger optimizer systems measure the boards transversely and then position the flitch onto a feeding mechanism and move the flitch longitudinally into the edger. This conventional method requires a considerable amount of expensive scanning, positioning and transporting equipment to carry out the process. Conventional systems also commonly create cumulative scanning, positioning and transport errors that make the systems somewhat less than optimal. With regard to the '557 patent, complex board centering mechanisms, multiple scanner heads, complex and high maintenance feeding and tracking devices, and complex high inertia edger rotation devices are all characteristic of the system described in the patent.
U.S. Pat. Nos. 5,761,979 and 5,870,936 to McGehee and incorporated herein by reference, disclose using a saw guide or saw guides where sawguides and saws are actively translated along a fixed driven arbor. The sawguides and saws may be skewed a few degrees on either side of the perpendicular to the arbor axis, so that the saws either actively traverse a non-symmetrical flitch fed into the saws lineally for optimum board edging, or actively follow a curved path for sawing boards from a cant fed into the saws lineally, from optimized data of the scanned profile. This system permits curve sawing without requiring the movement of the entire saw box.
U.S. Pat. No. 7,013,779 to McGehee et al and is incorporated herein by reference, discloses a sawguide and saw assembly that includes a plurality of sets of sawguides operating on corresponding saws mounted on a common saw arbor, wherein the sawguides within each set positioned adjacent to one another to create an array of laterally-abutting sawguides. Corresponding sawguide biasing assembly's bias the sawguides in each set against one another. The arrays are supported for independent movement along a lateral path generally parallel to the axis of the arbor. Lateral drivers are used to move each array in unison along the lateral path but independent of the other arrays. A sawguide array skewing assembly couples the sawguides of each array to one another so that the sawguides can be pivoted in unison about their respective pivot axes by a corresponding skewing driver.
In addition, many conventional curve edging systems are limited in terms of the width of boards that may be cut from a flitch. Such boards are limited by the width of the narrowest portion of the flitch. As the edging saws approach the narrowest portion of the flitch, their mounting on a common arbor prevents any ability to overlap the saw blades. Accordingly the cumulative width of boards cut from a flitch must be less than the narrowest portion of the flitch. However, it will be appreciated that these board widths may not correspond to the maximum widths available to be cut form a flitch based upon the usable sapwood of the flitch.